The present invention relates to an axial-flow fan unit and a heat-emitting element cooling apparatus which uses the axial-flow fan unit, for cooling a heat emitting element such as an electronic component.
Such a heat-emitting element cooling apparatus has been know that includes a heat sink having a base and a plurality of radiation fins, and a fan unit. In this apparatus, a heat-emitting element to be cooled is mounted on the rear surface of the base, and the plurality of radiation fins are fixed to the base. The fan unit is disposed above the heat sink, for blowing air along at least the radiation fins to promote heat dissipation from the radiation fins. In this heat-emitting element cooling apparatus, heat generated from the heat-emitting element is transferred from the base to the radiation fins. Then, the air flowing from the fan unit along the radiation fins carries away the heat of the radiation fins, thereby cooling the heat-emitting element.
U.S. Pat. No. 6,407,913 discloses an electronic component cooling apparatus where a heat sink provided with a plurality of radiation fins juxtaposed on a base, is cooled by a fan unit.
Japanese Patent Application No. 267093/2002 (Laid-Open Publication No. 104020/2004), which is the prior application of the applicant of the present invention, discloses an axial-flow fan unit in which the shape of a venturi is so defined that, as seen from the radially outward direction of the revolving shaft of a motor for rotating an impeller, part of a plurality of blades located on the side of the motor can be seen.
Further, U.S. Design Pat. No. 441,724 and U.S. Design Pat. No. 450,306 disclose a heat sink constituted by a radiation group comprising four space-dividing radiation fins and a plurality of subdividing radiation fins. In this heat sink, the four space-dividing radiation fins directly extend from the outer periphery of a base in the radial direction of the revolving shaft of a motor, thereby dividing a space surrounding the outer periphery of the base into four spaces. The plurality of subdividing radiation fins are located within the divided spaces in order to further subdivide the divided spaces. A part of the subdividing radiation fins respectively extend outward from two of the space-dividing radiation fins adjacent to each other, and the remaining subdividing radiation fins respectively extend outward from the outer periphery of the base located between two adjacent space-dividing radiation fins.
Like the axial-flow fan unit as shown in Japanese Patent Application No. 267093/2002 (Laid-Open Publication No. 104020/2004), in which the shape of the venturi is so defined that part of a plurality of blades located on the side of the motor can be seen as viewed from the radially outward direction of the revolving shaft of the motor for rotating the impeller, comparatively large noise might be produced.